Storage of electric power allows low-value power produced “off-peak” (e.g., overnight) to be released during “peak” power demand periods (e.g., daytime) when the value of power is substantially higher and when power shortages are most likely to occur. This is true regardless of the source (e.g., coal-fired power, nuclear power, wind power, etc.) of the “original” power to be stored. Numerous important benefits result from multi-megawatt (“bulk”) power storage methods, including using off-peak energy to provide more peak power, expanding the amount of higher-value peak power that can be delivered through existing transmission and distribution infrastructure, and transforming intermittent (unreliable) power sources such as wind and solar into “firm,” “dispatchable” (reliable) sources.
Generally, electrical grids can only tolerate +/−10% intermittent renewable power as a percentage of the total power supply on the grid, because allowing significantly more intermittent power would cause the grid to become unstable/unreliable and may “crowd-out” the more reliable (and thus more valuable) power from baseload plants. This represents a “ceiling” for the market penetration of intermittent renewable power sources in the absence of a cost-effective, broadly deployable bulk power storage solutions such as the disclosed embodiments. In addition, smaller multi-megawatt energy storage systems (e.g., 1 MW to 50 MW) provide a means to add peak power capacity to constrained load pockets at high net efficiency while helping to upgrade (and, in effect, expand) power distribution systems, especially in areas where few other options exist and/or where upgrades are costly.
There are many benefits of bulk power storage to the electrical grid, including but not limited to the ability to buy electric energy low (off-peak) and sell high (peak), greater electric supply capacity, elimination of the need for “peaker” power plants, reduction of transmission capacity requirements and congestion, better electric service reliability and power quality, reduction in electric bills, and firming of renewables capacity. Not all of the above power storage values apply for each deployment of a storage asset, because the individual values that can be garnered are case-specific. However, as a general rule, the closer the power “release” of a power storage system is to the load, the more benefit it will bring to the overall electrical grid, including but not limited to, utilities, ISOs and rate-payers. Thus, systems such as the disclosed embodiments whose power release can occur close to the power load are more valuable than those that can only be deployed far “upstream” on the grid.
Despite the many advantages of bulk power storage identified above, there are very few market-ready power storage options in the lower commercial scale range, e.g., 1 MW to 50 MW. Battery technologies are generally limited to a few MW/MWH of capacity (under 5 MW/10 MWH per day) and have other drawbacks including disposal issues at the end of the life of the batteries and limited discharge durations (generally less than 2 hours per day). There are several available methods for large, utility-scale (greater than 100 MW) power storage, including Compressed Air Energy Storage (CAES), pumped hydro, and liquid air energy storage (LAES) such as Vandor's Power Storage (VPS) Cycle. CAES is severely limited by the need for caverns and/or other underground geological formations that are required to contain the compressed air. Also, CAES does not deliver a consistent amount of power output; rather, the amount of power generated declines with each hour of power release, as the pressure of the compressed air in the cavern decreases throughout the daily cycle. Pumped hydro is also limited by geography and geology, requiring two large “lakes” to be separated by a significant height differential between the two reservoirs, with a dam and water-turbines between them.
VPS is much more flexible because it is not constrained by geography/geology and can be placed near the end user of the power, i.e., at the load, thus enhancing the deployment's value. However, in order to increase the total number of possible deployment sites, the basic principles of VPS, and the methods and systems embodied in the previous patents, need to be enhanced to allow for the technology to be deployable not only at utility scales, (which can be characterized as approximately 50 MW/400 MWH and larger), but also at smaller, “commercial scales,” which will typically be as small as about 1 MW, but could be even smaller, i.e., in the kW scale. A network of widely deployed, smaller-than utility-scale, power storage facilities will constitute a “distributed power storage” system. Such a system offers many benefits, including flexibility as to how the inflow to storage occurs on the grid and as to how the outflow from storage is sent out to power users.
The various pumped hydro, and the two CAES deployments now operating worldwide, are the largest-scale examples of power storage, where each deployment can send out hundreds of megawatts of power. At the other end of the scale, proposals have been put forth for using the power storage capacity of the batteries in all-electric cars as a “crowd source” distributed power network where each car provides only a few kW of power output (when it is plugged in to a two-way connection to the grid), but where the cumulative effect of many such plugged in cars may be significant. Thus, there is a need for an energy storage system that fits within the gap that exists between those two extremes, and which gap is not now served by commercially viable technologies.
In addition to the power storage issues outlined briefly above, the power distribution network faces another set of related challenges that are best solved by “distributed power generation” systems and methods. For example, if the power distribution network is to be more reliable, it needs to be restructured. In particular, there is a need for an energy production and distribution system that relies less on large-scale, centralized power plants located far from their customers, where an increasingly congested and vulnerable (to natural and man-made events) grid connects large generating facilities with a customer base. Instead, there is a need for power generation that can be employed at lower capital cost and more locally, near customers, providing for redundancy, shorter travel times/distances on the grid (reducing line losses and congestion), and allowing for more competition in the market and at a pricing structure that reflects the multiple options for localized (distributed) power production. The smaller the economic and technical “threshold” for distributed power production systems the more widely they can be deployed, the more “distributed” the deployments, the more such a network can avoid grid congestion, and the less vulnerable the grid becomes to unplanned natural and man-made outages i.e., by relying on numerous widespread generation sources instead of just one (or several) large, centralized power plants).
Accordingly, there is a need for power storage systems and methods, which can transform low-value, off-peak power into high-value peak power and which can make intermittent power sources “firm.” There is a further need for power storage and distributed generation systems and methods that can be widely deployed at smaller commercial scales. Finally, There is also a need for power storage and distributed generation systems and methods, which can be located close to power consumers (i.e., load centers).